Subject: Re: [mobile-ip] Mobile Prefix Advertisements

From: [email-masked]
Date: Fri, 27 Sep 2002 10:58:37 +0530

Hi,

In draft-18 it is specified that "HomeRtrAdvInterval" is 3,600 seconds.
That means the RA's in the Home link should be sent every 3,600 secs. But
for Mobile IPv6 specified value for "MaxRtrAdvInterval" is only 1.5 secs.
And you have said that - "MaxRtrAdvInterval is the maximum value for
HomeRtrAdvInterval". Do we need to change any of those values ?

- Sourajeet

                      "T.J. Kniveton"                                                                             
                      <[email-masked]>               To:       [email-masked]                 
                      Sent by:                        cc:       [email-masked]                     
                      owner-mobile-ip@sunroof.        Subject:  Re: [mobile-ip] Mobile Prefix Advertisements      
                      eng.sun.com                                                                                 

                      25/09/2002 10:43 PM                                                                         

[email-masked] wrote:
>
> Hi,
>
> With reference to draft-18, I have some doubts regarding Mobile Prefix
> Advertisements

Sorry that it is not fully clear. I will try and answer your questions
below.

>
> Section 10.9.2 : Scheduling Prefix Deliveries to the Mobile Node
>    "The home agent uses the following algorithm to determine when to send
>    prefix information to the mobile node.
>
>     -  If the mobile node has not received the prefix information within
>        the last HomeRtrAdvInterval seconds, then transmit the prefix
>        information.  This MAY be done according to a periodically
>        scheduled transmission."
>
> 1) What is "HomeRtrAdvInterval" and how it is communicated to MN?Is it a
> contant value?

It is the Home Router Advertisement Interval. I.e., the interval at which
Router Advertisements are sent on the home network. Yes, it is a constant
value
based on the configuration of the home agent.

>
> Section 11.3.3: Sending Mobile Prefix Solicitations
>    "The mobile node SHOULD send a Solicitation to the home agent when
>    its home address will become invalid within MaxRtrAdvInterval
>    seconds, where this value is acquired in a previous Mobile Prefix
>    Advertisement from the home agent.  If no such value is known, the
>       value MAX_PFX_ADV_DELAY seconds is used instead (see section 12)."
>
> 2) How "MaxRtrAdvInterval" is conveyed to MN? Is it through
> "AdvIntervalOption"?

Yes, it could be conveyed through that option.

> 3) What should be the value of "MaxRtrAdvInterval"?

In section 7.5, MaxRtrAdvInterval is defined.

>
> For Mobile IPv6 the MaxRtrAdvInterval is 1.5 secs.

Yes, this is true, and this is a problem. The MPAs should be sent
periodically,
but not nearly that often. I will address this in another, follow-up
e-mail.

>
> 4) How MaxRtrAdvInterval is similar to MAX_PFX_ADV_DELAY ?

Here is my personal interpretation:

MaxRtrAdvInterval is the maximum amount of time that the Home Agent should
wait
in between sending Router Advertisements on the home link.
MAX_PFX_ADV_DELAY is
the maximum amount of time it is estimated that prefix advertisements will
be
delayed in transit. MaxRtrAdvInterval is more related to the
characteristics of
the network, as in how often prefixes might change, how likely it is for a
node
to spontaneously turn on or lose its prefix information, etc.
MAX_PFX_ADV_DELAY, on the other hand, is solely related to the latency,
distances between nodes, and number of gateways in the network.

This is unrelated to the question you asked above, about what MPAs should
use,
which I will write another e-mail about as promised.

>
> In my opinion "MaxRtrAdvInterval" should be "HomeRtrAdvInterval". Please
> correct me if i am wrong.

No, the HomeRtrAdvInterval is the amount of time between RAs. The
MaxRtrAdvInterval is the maximum value for HomeRtrAdvInterval.

> thanks
> Sourajeet...

-TJ

--
        T.J. Kniveton
   Communication Systems Lab
     Nokia Research Center

---

From: "T.J. Kniveton" <[email-masked]>
Date: Fri, 27 Sep 2002 14:16:13 -0700

> HomeRtrAdvInterval". Do we need to change any of those values ?

This seems to be a confusing issue. Let me try and answer it again and give a
more historical motivation (if you skim this, please read the 5
comments/questions at the end):

First, MinRtrAdvInterval and MaxRtrAdvInterval are the two limits in Neighbor
Discovery which govern how often Router Advertisements should be sent by a
router. In Mobile IPv6, these limits are relaxed (i.e. lowered) more than in
usual neighbor discovery, in order to allow Access Routers (and Home Agents)
which serve a mobile node to send RAs quite frequently. This lets the MN use
the RAs as a guide in movement detection.

So MinRtrAdvInterval and MaxRtrAdvInterval are the bounds of how often an RA
should be sent by an Access Router on a link serving Mobile Nodes. The value
ranges from 50 ms - 1.5 s.

					ooo

OK, now that that's clear, let's have a flashback..

Back in their former incarnation, MPAs were called Tunneled Router
Advertisements. So if I say Tunneled Router Advertisement, in today's world,
substitute in "Mobile Prefix Advertisement." At that point in the past, there
were two values (defined in draft-13), which were HomeRtrAdvInterval, and
MAX_PFX_ADV_DELAY, and both were defined as 1,000 seconds.

It was specified that a Tunneled Router Advertisement should be send at least
every HomeRtrAdvInterval (1000s), or whenever solicited. So basically, this
amounts to a MaxRtrAdvInterval for Tunneled Router Advertisements. (Forget what
I said about Min~ and Max~ bounding this value; that was wrong.)

Back in the earlier drafts, MAX_PFX_ADV_DELAY was used by the mobile node to
estimate how often the Tunneled Router Advertisements would be sent out, so
that the MN could know if its home address was going to expire before the next
anticipated tunneled RA, and send a Router Solicitation (now Mobile Prefix
Solicitation) to the Home Agent.

MAX_PFX_ADV_DELAY was also used (as it is now) to compute the offset that
should be used for sending Tunneled Router Advertisements. As I look at this
formula, I can't help but think that this is the wrong value to use;
HomeRtrAdvInterval would be the correct one. Since they were both the same back
then, it didn't matter.

					ooo

Now, back to the present. Obviously, things were changed quite a bit in
draft-14, and out of that we have the Mobile Prefix Solicitation and
Advertisement. We still use these two values, but HomeRtrAdvInterval was
changed to 10 minutes.

If we update the values for HomeRtrAdvInterval and change its name, and change
the formulae for MAX_SCHEDULE_DELAY and RAND_ADV_DELAY, we can forget about
using a minimum threshold (as I suggested in 15 seconds), since this will be
embodied by these changes.

It would be nice if we could have some input on these formulae. Here are some
proposed changes to synchronize everything and some questions:

- HomeRtrAdvInterval should be renamed, perhaps to MaxMobPfxAdvInterval

- formula for MAX_SCHEDULE_DELAY should use MaxMobPfxAdvInterval instead of
MAX_PFX_ADV_DELAY

- Is there some reason why we need a separate variable, MAX_PFX_ADV_DELAY? It
seems like it should always be equal to MaxMobPfxAdvInterval. Correct? Maybe we
can just get rid of it and the mobile node can use the same value defined for
the latter.

- RAND_ADV_DELAY uses MinRtrAdvInt. But this is for router advertisements at
the home agent. Perhaps we also need to define a MinMobPfxAdvInterval to set
the min bound for MPAs.

- What should the best values for {Max,Min}MobPfxAdvInterval be?

Hope that is a better explanation!

-TJ

---

From: Joe Lau <[email-masked]>
Date: Fri, 27 Sep 2002 16:19:28 -0700 (PDT)

Francis,

Your draft, Using IPsec to Protect MIPv6 Signalling between MN and HA,
does not mention if the MN-HA tunnel will be torn down when the MN returns
home.  Can you shed some light on this issue?

Regards,

Joe Lau

Francis,

Your draft, Using IPsec to Protect MIPv6 Signalling between MN and HA,
does not mention if the MN-HA tunnel will be torn down when the MN returns
home.  Can you shed some light on this issue?

Regards,

Joe Lau

---

From: Francis Dupont <[email-masked]>
Date: Sat, 28 Sep 2002 16:09:14 +0200

=> home deregistration will delete the tunnel at the HA side.
IMHO the SPD entries should be removed too when no packets will be
still in transit. SAs are less important but there is some good reasons
to keep the SA pairs for BU/BA (it is very specific and can be used again).

Regards

[email-masked]

---

From: Jari Arkko <[email-masked]>
Date: Sat, 28 Sep 2002 20:28:32 +0300

> to keep the SA pairs for BU/BA (it is very specific and can be used again).

The BU/BA protection stays as it is, it is also needed on the home link
and it is not dependent on care-of addresses.

The protection within the tunnel is implicitly made inactive by the fact
that the mipv6 tunnel itself no longer exists and the SPD entries said "interface
is the tunnel to the mn/ha". The IPsec tunnel may be deleted or kept; what
matters is that by the time we are at a new location the tunnel gw is set
correctly again on the HA side.

All SAs created through IKE can stay as they are, automatically deleted
when they expire or taken back to use when there is a need to do that
again.

Jari

---

From: Michael Thomas <[email-masked]>
Date: Sat, 28 Sep 2002 12:16:09 -0700 (PDT)

> to keep the SA pairs for BU/BA (it is very specific and can be used again).

   I don't understand. Why should MIP and IPsec be
   coupled in this manner? The desire to have a SA
   seems pretty orthogonal to the desire to use 
   something as a HA.

		Mike

---

From: Vladislav Yasevich <[email-masked]>
Date: Mon, 30 Sep 2002 11:27:57 -0400

TJ

I agree with you in genral.  This should be clarified.

> - formula for MAX_SCHEDULE_DELAY should use MaxMobPfxAdvInterval instead of

That makes sense, but see blow...

> can just get rid of it and the mobile node can use the same value defined for

The MAX_PFX_ADV_DELAY variable is the default for the Mobile Node when it
doesn't know what the actual prefix advetisement interval is
(it hasn't received an MPA that specified it).

Having said that, as long as the mobile node knows the {Min,Max} defaults
definded below, this variable can be removed.

> the home agent. Perhaps we also need to define a MinMobPfxAdvInterval to set

Yes.

> - What should the best values for {Max,Min}MobPfxAdvInterval be?

Why not re-use the valudes defined in 2461 for {Max,Min}RtrAdvInterval.
We are essentially trying to reproduced the same functionality.

-vlad
++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++
Vladislav Yasevich		Tru64 UNIX - IPv6 Project Lead
Hewlett Packard 		Tel: (603) 884-1079
Nashua, NH 03062		ZKO3-3/T07